U.S. patent application number 14/556313 was filed with the patent office on 2015-06-25 for radial impeller for a drum fan and fan unit having a radial impeller of this type.
The applicant listed for this patent is ebm-papst Mulfingen GmbH & Co. KG. Invention is credited to Katrin BOHL, Daniel GEBERT, Erik REICHERT.
Application Number | 20150176594 14/556313 |
Document ID | / |
Family ID | 51904716 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150176594 |
Kind Code |
A1 |
GEBERT; Daniel ; et
al. |
June 25, 2015 |
RADIAL IMPELLER FOR A DRUM FAN AND FAN UNIT HAVING A RADIAL
IMPELLER OF THIS TYPE
Abstract
An impeller has an inlet and outlet. A bottom disc has an
external diameter. A top disc concentric to the bottom disc at an
axial distance therefrom has a suction opening for the inlet. A
plurality of forward-curved blades are arranged between the bottom
disc and the top disc. A flow channel has an inner inlet side and
an outer outlet side formed between adjacent blades. The channel is
curved convexly viewed in the running direction of the impeller.
The external diameter of the bottom disc is at least 20% greater
than the internal diameter of the suction opening. The top disc
forms a guiding surface and an angle is formed between a tangent on
the guiding surface at the inlet to the suction opening and a
tangent on the guiding surface at the outlet from the flow channel
on the air outlet side is at least 30.degree..
Inventors: |
GEBERT; Daniel; (Ohringen,
DE) ; BOHL; Katrin; (Kunzelsau, DE) ;
REICHERT; Erik; (Boxberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ebm-papst Mulfingen GmbH & Co. KG |
Mulfingen |
|
DE |
|
|
Family ID: |
51904716 |
Appl. No.: |
14/556313 |
Filed: |
December 1, 2014 |
Current U.S.
Class: |
416/186R |
Current CPC
Class: |
F04D 29/681 20130101;
F04D 17/08 20130101; F04D 29/30 20130101; F04D 29/282 20130101;
F04D 29/667 20130101; F04D 29/22 20130101; F04D 29/4226 20130101;
F04D 29/4233 20130101; F04D 29/441 20130101 |
International
Class: |
F04D 29/22 20060101
F04D029/22; F04D 29/44 20060101 F04D029/44; F04D 17/08 20060101
F04D017/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2013 |
DE |
10 2013 114 609.0 |
Claims
1. A radial impeller having an axial air inlet and an air outlet
over an impeller circumference, preferably for use in a spiral
housing, the radial impeller comprising: a bottom disc which has an
external diameter, a top disc which is arranged concentrically to
the bottom disc at an axial distance therefrom and has a circular
suction opening with an internal diameter for the axial air inlet,
and a plurality of forward-curved, profiled blades arranged between
the bottom disc and the top disc, a flow channel having a radially
inner air inlet side and a radially outer air outlet side being
formed between two adjacent blades in each case, which channel is
curved convexly, viewed in the running direction of the radial
impeller, wherein the external diameter, of the bottom disc, based
on the internal diameter of the suction opening, is at least 20%
greater than the internal diameter of the suction opening, in that
the top disc forms a top guiding surface for the flow channel, an
angle which opens towards the inlet opening and is formed between a
tangent on the top guiding surface at the inlet to the suction
opening of the top disc and a tangent on the top guiding surface at
the outlet from the flow channel on the radially outer air outlet
side thereof, being at least 30.degree..
2. The radial impeller according to claim 1, wherein the external
diameter of the bottom disc, based on the internal diameter of the
suction opening, is at least 50%, but at most 90% greater than the
internal diameter of the top disc.
3. The radial impeller according to claim 1, wherein in the
profiled blades, a profile thickness ratio of maximum profile
thickness to profile overall length is at least 0.15, in particular
at least 0.2 and more preferably at least 0.25, the profile
thickness ratio being at most 0.5 and in particular 0.4, more
preferably 0.35.
4. The radial impeller according to claim 1, wherein an inner
radius on the leading edge of the blades in the vicinity of the top
disc is greater than or equal to the inner radius of the suction
opening in the top disc.
5. The radial impeller according to claim 1, wherein an outlet
diameter of the blades on the top disc is less than or equal to the
external diameter of the top disc and/or is less than or equal to
the external diameter of the bottom disc.
6. The radial impeller according to claim 1, wherein a number of
blades is at least 19 and at most 54 and is preferably within a
range of 22 to 46.
7. The radial impeller according to claim 1, wherein the top disc,
the blades and the bottom disc are configured as a composite body
consisting of two parts, in particular of two plastics
injection-moulded parts which are integrally bonded.
8. The radial impeller according to claim 1, wherein the bottom
disc forms a bottom guiding surface in the flow channel.
9. The radial impeller according to claim 1, wherein the top
guiding surface and/or the bottom guiding surface of the flow
channel have a constant curvature.
10. The radial impeller according to claim 1, wherein in each case
the leading edges of the blades on the radially inner air inlet
side and/or the trailing edges of the blades on the radially outer
air outlet side are rounded.
11. The radial impeller according to claim 1, wherein the cross
section of the flow channel tapers from the radially inner air
inlet side to the radially outer air outlet side, in particular a
shortest distance between the bottom disc and the top disc
decreasing in the flow direction.
12. The radial impeller according to claim 1, wherein an impeller
outlet width on the radially outer air outlet side of the flow
channel has a value which is at most 70% of an overall width of the
radial impeller.
13. The radial impeller according to claim 1, wherein the overall
width thereof is within a range of 25% to 70%, based on the
external diameter of the bottom disc.
14. The radial impeller according to claim 1, wherein the angle
which opens out towards the inlet opening and is formed between a
tangent on the top guiding surface at the inlet to the suction
opening of the top disc and a tangent on the top guiding surface at
the outlet from the flow channel on its radially outer air outlet
side is at most 90.degree., preferably at most 75.degree..
15. A fan unit, in particular a drum fan, having a radial impeller
according to claim 1, wherein the radial impeller is arranged in a
housing, in particular in a spiral housing.
16. The fan unit according to claim 15, wherein an inlet of the
housing for the radial impeller is nozzle-shaped, the inlet of the
housing in particular dipping into the suction opening in the top
disc.
17. The fan unit according to claim 15, wherein a ratio of a width
of the housing at the air inlet opening thereof into an air guiding
channel to an impeller outlet width of the radial impeller at the
radially outer air outlet side of the flow channel has a value
within a range of 1.0.ltoreq.V.sub.B.ltoreq.1.4.
18. The fan unit according to claim 15, wherein the radial impeller
is arranged in the housing coaxially with an electric drive motor,
an outer contour of the drive motor engaging positively in a motor
receiving opening in the bottom disc or being covered by a
full-surface bottom disc, and the bottom disc, preferably together
with the contour of the motor received in the motor receiving
opening thereof, having a dome-shaped formation.
19. The fan unit according to claim 15, wherein the housing has an
air guidance channel, wound spirally around the radial impeller,
with an oval cross section which increases constantly from the side
of the radial impeller.
Description
FIELD
[0001] The present disclosure relates to a radial impeller having
an axial air inlet and air outlet over the circumference of the
impeller, preferably for use in a spiral-shaped housing, comprising
a bottom disc which has an external diameter, and comprising a top
disc which is arranged concentrically to the bottom disc at an
axial distance therefrom and has a circular suction opening with an
internal diameter for the axial air inlet, and also comprising a
plurality of forward-curved, profiled blades arranged between the
bottom disc and the top disc, a flow channel having a radially
inner air inlet side and a radially outer air outlet side being
formed between two adjacent blades in each case, which channel is
curved convexly, viewed in the running direction of the radial
impeller. This channel curvature means that the suction-side
surfaces of the blades are curved in a convex manner, at least in
regions, and their pressure-side surfaces are curved in a concave
manner, at least in regions.
[0002] The disclosure also relates to a fan unit, in particular to
a drum fan, having a radial impeller of this type. The term "fan"
subsumes fans having a pressure ratio between suction side and
pressure side within a range of 1.0 to 1.1, as well as fans having
a pressure ratio between suction side and pressure side within a
range of 1.1 to 3.0.
BACKGROUND
[0003] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0004] Nowadays, radial impellers are preferably used where a high
build-up of pressure is to be achieved with a relatively low volume
flow. Since in the case of radial impellers, the entire conveyed
air flow leaves the impeller at the external diameter, it is
possible to generate a greater kinetic energy of the air molecules
and thereby also a higher pressure compared to an axial fan, the
circumferential speed of which is restricted at the wheel hub. The
use of radial impellers is particularly effective when an air flow
has to be diverted by 90.degree. from the axial direction into the
radial direction, or when components, filters or the like obstruct
a free air flow. The most common configuration is that of a
complete radial fan with a housing, although there are also
different motor-impeller combinations for uses in which the air
conveyance for the build-up of pressure can be integrated into one
device.
[0005] In the case of radial impellers, a distinction is made
between impellers with blades which are curved forwards in the
running direction, those with backward-curved blades and those with
radially ending blades. Blades which are curved forwards, in the
direction of rotation, cause the flow channel which runs from a
radially inner air inlet side to a radially outer air outlet side,
to be curved in a convex manner, viewed in the running direction of
the radial impeller. The suction-side surfaces of the blades are
thus curved in a convex manner, at least in regions, and their
pressure-side surfaces are curved in a concave manner, at least in
regions. Radial impellers having forward-curved blades allow a high
angular momentum to be delivered to the air flow and thus achieve a
high energy conversion. However, a disadvantage here is a high
dynamic pressure of the outgoing air. This dynamic pressure has to
be converted into static pressure in a subsequent guiding
apparatus, for example in a spiral housing. Radial impellers with
forward-curved blades deliver more angular momentum to the flow
than radial impellers with backward-curved blades. Thus, the
necessary speed for reaching the same operating point in radial
impellers with forward-curved blades is substantially lower
compared to radial impellers with backward-curved blades of the
same size. The efficiency of radial impellers having
backward-curved blades is significantly higher compared to radial
impellers having forward-curved blades.
[0006] A particular configuration of the radial fan is the drum
fan. Designated as drum fans are radial fans, the impellers of
which are identical to a drum, i.e. the width of the impeller is
relatively large compared to the diameter thereof. In particular,
it can be within a range of from 40 to 80 percent, based on the
external diameter of the bottom disc. Rotors of this type, provided
with forward-curved blades and also known for about 80 years under
the name of Scirocco rotors, are used where small radial dimensions
are required. The ratio of the internal diameter of the top disc to
the external diameter of the bottom disc of the original Scirocco
rotor was 0.875.
[0007] Present-day forward-curved radial impellers which are used
in spiral housings as cylindrical rotors are distinguished by a
high power density, i.e. by a high conveyed volume with a small
installation space and by good acoustic characteristics, in
particular by a low noise level during operation. However, the
aerodynamic efficiency is relatively low compared to
backward-curved impellers due to burbling and vortex formation.
Cylindrical rotor fans are used in ventilation and air-conditioning
technology in installations requiring a pressure increase of
preferably up to 4000 Pa and with volume flows of up to 8
m.sup.3/s, based on an impeller diameter of one metre and a
single-flow configuration.
[0008] In a radial impeller known, for example, from DE 10 2006 031
167 A1 of the type mentioned at the outset, having an axial air
inlet and air outlet over the circumference of the impeller, a
strong profiling of the blades can prevent or minimise burbling in
the flow channel between the blades. In this respect, "profiling"
means that the thickness of the blades varies over the extension
direction thereof, the blades more particularly then being
considered as strongly profiled when a so-called profile thickness
ratio therein, i.e. a ratio of profile thickness to overall profile
length, is more than or equal to 0.15, in particular more than or
equal to 0.2 and more preferably more than or equal to 0.25. In
this respect, the profile thickness ratio is preferably at most
0.5, in particular 0.4 and more preferably 0.35. The top disc not
shown in the figures of the mentioned document is called a frame in
said document and is part of the spiral housing. Burbling at the
top disc is disadvantageously reinforced by the known blade
profiling. Thus, this measure can only very slightly increase the
efficiency.
SUMMARY
[0009] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0010] The object of the present disclosure is to provide a radial
impeller of the type mentioned at the outset and a fan unit having
a radial impeller of this type, in which the advantages of a
cylindrical rotor are combined with the advantages of an impeller
of this type having backward-curved blades, thus with which it is
possible to achieve in particular an increase in efficiency while
retaining a high power density and a low development of noise.
[0011] This is achieved according to the disclosure in that the
external diameter of the bottom disc of the radial impeller, based
on the internal diameter of the suction opening, is at least 20%
greater than the internal diameter of the suction opening, in that
the top disc forms a top guiding surface in the flow channel, an
angle which opens out towards the inlet opening and is formed
between a tangent on the top guiding surface at the inlet to the
suction opening of the top disc and a tangent on the top guiding
surface at the outlet from the flow channel on the radially outer
air outlet side thereof, being at least 30.degree..
[0012] A fan unit according to the disclosure is distinguished in
that the radial impeller according to the disclosure is arranged in
a housing, particularly in a spiral housing.
[0013] Due to the disclosure, it is possible to retain the
advantage of radial impellers known hitherto as cylindrical rotors,
in that these have a high power density and a low noise with slight
rotational noise increases compared to radial impellers having
backward-curved blades. The advantageously high power density can
be attributed to a high angular momentum delivered to the flow by
the forwards curvature of the blades. In this respect, a low
development of noise is promoted by preferably high numbers of
blades and preferably low speeds during operation. Both the
forwards curvature and particularly also a large number of blades
prevent or reduce at least burbling at the blades and at the top
disc, but they increase the friction forces, which can lead to
losses and to a reduction in efficiency. This can be effectively
counteracted by the geometric configuration according to the
disclosure of the radial impeller, and a preferred configuration
can provide that the external diameter of the bottom disc, based on
the internal diameter of the suction opening of the top disc, is
greater by 50%, at most by 90%, than the internal diameter of the
top disc.
[0014] The configuration according to the disclosure of the
diversion of the axial onflow into a radial or diagonal direction
can prevent in particular burbling at the top disc, which can be
detected by a so-called CFD flow simulation. CFD (computational
fluid dynamics) denotes a method which is established in flow
mechanics and has the objective of solving fluid-mechanical
problems iteratively by numerical methods and then visualising the
results, preferably by colour representations. In this respect, the
Navier-Stokes equations used in fluid mechanics and describing
momentum conservation and mass conservation are modelled
mathematically while presetting specific marginal conditions. This
is an economical alternative to expensive experimental test series
which are carried out, for example in a wind tunnel, and it makes
it possible to analyse flow parameters which cannot be determined
by measurements, such as turbulent kinetic energy, vortex
viscosity, etc.
[0015] To prevent burbling at the top disc, a configuration of the
top disc with a preferably relatively great axial width is also
significant, according to which configuration the width of the top
disc can preferably occupy at least 30% of the overall width of the
impeller. A width configuration of this type is to be considered as
being synergistically effective in combination with the disclosure,
since in the case of conventional cylindrical rotors with
unprofiled blades, an improvement cannot be achieved by this
configuration.
[0016] With a predetermined shaft output, the efficiency is
determined by the conveyed volume flow and by the total pressure
increase caused by the fan, the product of which gives the
conveying capacity, the term "total pressure" being understood as
meaning the sum of static and dynamic pressure according to the
so-called Bernoulli equation. Thus, the efficiency describes the
ratio of conveying capacity to power of a shaft driving the fan and
is calculated according to the formula:
.eta.=(V*.DELTA.p.sub.t)/P.sub.W
where .eta. denotes the non-dimensional efficiency, V denotes the
volume flow in m.sup.3/s, .DELTA.p.sub.t denotes the total pressure
increase in Pa and P.sub.W denotes the shaft output in W.
[0017] The combination of the "profiled blades" feature with the
features of the top disc configured in terms of flow according to
the disclosure can significantly increase the efficiency. However,
this is only possible when the external diameter of the bottom disc
is at least 20% greater than the internal diameter, determining the
size of the suction opening, of the top disc, in contrast to the
previous known embodiments.
[0018] On the other hand however, with unprofiled blades, as are
also known from the prior art, it is not possible, even with the
diameter ratio provided according to the disclosure and the minimum
angle between the tangents of 30.degree., to divert the flow in the
blade channel without any burbling. As is known, burbling involves
losses and results in poor impeller efficiency. Thus, as is known,
it is even assumed that an imperfect onflow at the blade inlet due
to excessively steep blades is still to be considered as more
favourable than an unstable burbling which occurs in a
blade-congruent flow. Due to a blade profiling, the flow can be
deflected in the blade channel without any burbling in the
configuration, provided according to the disclosure, of top disc
and bottom disc, in spite of a blade-congruent onflow, which
implies low impact losses at the blade inlet.
[0019] It is possible to further increase the efficiency of an
entire fan with the radial impeller according to the disclosure by
selecting a width ratio of a housing width at the impeller outlet
to the impeller outlet width itself of at least 1.0 to at most
1.4.
[0020] Thus, with the disclosure it is possible to achieve
efficiencies within a range of between 0.65 and 0.80, preferably
even up to 0.90.
[0021] When a backward-curved radial fan according to the prior art
is operated at the optimal acoustic operating point, i.e. at
maximum efficiency, it is possible to estimate the total sound
power level with an accuracy of .+-.4 dB according to the
formula:
L.sub.W=37+10 log(V)+20*log(.DELTA.p.sub.t).
[0022] In this formula, L.sub.W denotes the total sound power level
in dB, V denotes the volume flow in m.sup.3/s and .DELTA.p.sub.t
denotes the total pressure increase in Pa. However, this formula
cannot be applied to the radial impeller according to the
disclosure. Compared to the measured values or to the values which
are calculated according to the above L.sub.W formula, for radial
impellers according to the prior art, a radial impeller according
to the disclosure, for example with an external diameter of 170 mm
achieves an improvement of more than 4 dB in the acoustically
optimised operating range.
[0023] The coefficient of performance L which is to be considered
as an indication of the power density is understood, according to
the formula:
L=.phi..sub.r*.psi.
as the product of capacity coefficient .phi..sub.r and coefficient
of pressure .psi.. In this respect, all the quantities are
non-dimensional, the capacity coefficient .phi..sub.r being
calculated according to the formula:
.phi..sub.r=(V*60)/(b*.pi..sup.2*D.sup.2*n)
and describing the ratio of the actual conveyed quantity to the
theoretically possible conveyed quantity. The capacity coefficient
results from the product of the outlet surface of the wheel and of
the circumferential speed. In the formula, (Pr is the capacity
coefficient, the index r representing "radial", V is again the
volume flow in m.sup.3/s, D is the impeller external diameter in m
which is determined by the outlet diameter D.sub.a,S of the blades,
b is the outlet width of the impeller in m and n is the speed in
1/min.
[0024] The coefficient of pressure is the ratio of the pressure
level, generated by the wheel, to the dynamic pressure of the
circumferential speed and is calculated according to the
formula:
.PSI.=(.DELTA.p.sub.t*2*60.sup.2)/(p*(D*.pi.*n).sup.2)
where .PSI. is the non-dimensional coefficient of pressure, p is
the density in kg/m.sup.3, .DELTA.p.sub.t is the total pressure
increase in Pa, D is again the impeller external diameter in m
determined by the outlet diameter D.sub.a,S of the blades, and n is
the speed in 1/min.
[0025] With the disclosure, it is possible to achieve capacity
coefficients within a range of 0.6 to 1.0, preferably within a
range of 0.6 to 0.8 and coefficients of pressure within a range of
2.2 to 3.2, preferably within a range of 2.8 to 3.0, it being
possible for the coefficient of performance to be within a range of
0 to 1.5, preferably within a range of 0 to 1.0.
[0026] Unlike conventional cylindrical rotors in which, when the
impeller is installed, there is usually an axial distance in the
region of a few millimetres between nozzle and top disc; in the
configuration according to the disclosure of the top disc, it is
also optionally advantageously possible to provide a nozzle-shaped
configuration of the inlet and an axial dipping of the nozzle into
the top disc. Consequently, the split flow can be aimed in the same
direction as the main volume flow entering through the suction
opening. The split flow then advantageously contributes to the
stabilisation of the deflection into the radial direction, which,
as is known, only happens in the case of radial wheels with
backward-curved blades.
[0027] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0028] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0029] Advantageous configurations of the disclosure are contained
in the sub-claims and will be described in more detail with
reference to the embodiments shown in the accompanying drawings, in
which:
[0030] FIG. 1 is an axial part-sectional view of a preferred
configuration of a radial impeller according to the disclosure,
[0031] FIG. 2 is a view of a cross section along line II-II in FIG.
1, of the configuration of the radial impeller according to the
disclosure shown in FIG. 1.
[0032] FIG. 3 is similar to FIG. 1, but is a full sectional view of
the configuration of a radial impeller according to the disclosure
installed in a fan unit according to the disclosure,
[0033] FIG. 4 is an axial half-sectional view of a second
configuration of a radial impeller according to the disclosure in a
fan unit according to the disclosure,
[0034] FIG. 5 is a view, like that of FIG. 4, and simplified
compared to FIG. 3, of the first configuration of a radial impeller
according to the disclosure in a fan unit according to the
disclosure,
[0035] FIG. 6 is a view, like that of FIG. 1, of a second
configuration of a radial impeller according to the disclosure.
[0036] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0037] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0038] In the figures of the drawings, identical parts or
functionally identical parts are denoted by the same reference
numerals and signs. However, if specific, described features and/or
features which can be inferred from the drawings of the radial
impeller or fan unit according to the disclosure or the
constituents thereof are mentioned only in connection with the
embodiments, they are also, according to the disclosure and
independently of this embodiment, significant as individual
features or also combined with other features of the embodiment and
can be claimed as belonging to the disclosure.
[0039] As can firstly be seen from FIGS. 1 and 2, a radial impeller
10 according to the disclosure has a top disc 1, a plurality of
forward-curved, profiled blades 2 and a bottom disc 3. The top disc
1 forms a suction orifice and thus has a circular suction opening 4
with an internal diameter D.sub.i,DS for an axial air inlet. The
bottom disc 3 has an external diameter D.sub.a,BS and is arranged
concentrically to the top disc 1 at an axial distance
therefrom.
[0040] The blades 2 are located between the top disc 1 and the
bottom disc 3. Formed between two blades 2 in each case is a flow
channel 5 which, viewed in the running direction LR of the radial
impeller 10, is curved convexly and in which the flow moves in a
direction S from a radially inner air inlet side 5a to a radially
outer air outlet side 5b. The curvature of the flow channel 5,
which is convex at least in part, viewed in the running direction
LR of the radial impeller 10, means that, as shown in FIG. 2, a
pressure side 2c of the blades 2 which, viewed in the running
direction LR of the radial impeller 10, is respectively located
under the blades 2, is curved in a concave manner, at least in
part, and a suction side 2d of the blades 2 which, viewed in the
running direction LR of the radial impeller 10, is respectively
located on the blades 2, is curved in a convex manner, at least in
part.
[0041] The top disc 1, the blades 2 and the bottom disc 3 can
preferably be configured as a composite body consisting of two
parts, in particular of two plastics injection-moulded parts which
are integrally bonded.
[0042] Profiling of the blades 2 means that the profile thickness
d.sub.S of the blades 2 is not constant over the length thereof. In
this respect, characteristic of the profiling of the blades 2 is a
profile thickness ratio which is described by the ratio V.sub.P of
maximum profile thickness d.sub.S to profile overall length L.sub.S
(see in this respect FIG. 2) and which should be at least 0.15, in
particular at least 0.2, and more preferably at least 0.25, it
being possible for the profile thickness ratio V.sub.P to be at
most 0.5, in particular 0.4 and more preferably 0.35. The position
of the maximum profile thickness d.sub.S can preferably be within a
range of 5% to 75% of the profile overall length L.sub.S, seen from
the air inlet side 5a, and from there is reduced both towards the
leading edge 2a of the blades 2 and towards the trailing edge 2b.
The advantages described above come into effect as a result of this
particularly streamlined profiling, but according to the disclosure
without any burbling phenomena of the flow occurring on the top
disc 1.
[0043] To form a shape which is favourable in terms of
fluid-mechanics, it can be optionally provided, as shown in FIG. 2,
that the leading edges 2a and/or the trailing edge 2b of the blades
2 are rounded in each case. Further features which optionally or
preferably describe the shape of the blades are a crescent-shaped,
but asymmetrical cross section of the blades 2, an outer curvature,
which is convex at least in part, of the suction side 2d which is
greater than the inner curvature, which is concave at least in
part, of the pressure side 2c, and a drop shape in respect of the
curved centre axis through the blades 2.
[0044] An optimum number of blades 2, which number is
characteristically large for a drum fan, is at least 19 and at most
54 and is preferably within a range of 22 to 46. High numbers of
blades can block the flow channel 5 and reduce the maximum possible
volume flow V. In addition, the friction losses on the blade walls
can increase so that the efficiency .eta. decreases.
[0045] Furthermore, as can be seen in FIG. 3 and also in FIGS. 4
and 5, a radial impeller 10 according to the disclosure is
preferably intended for use in a fan unit 20 according to the
disclosure. The radial impeller 10 according to the disclosure can
be arranged in this fan unit 20 according to the disclosure,
preferably coaxially with an electric drive motor 6 and it is
positioned in a housing 7, which can preferably be a spiral-shaped
housing 7, as shown in FIG. 3.
[0046] In the illustrated configuration, the fan unit 20 according
to the disclosure is a fan having a forward-curved radial wheel. It
can preferably be a drum fan, a characteristic of which is also
that the overall width b.sub.ges of the radial impeller 10 is
within a range of 25% to 70%, based on the external diameter
D.sub.a,BS of the bottom disc 3. As shown in FIG. 1, the overall
width b.sub.ges is the sum of a width b.sub.DS of the top disc 1
and of an impeller outlet width b.sub.2 at the radially outer air
outlet side 5b of the flow channel 5.
[0047] According to the disclosure, it is provided that the
external diameter D.sub.a,BS of the bottom disc 3, based on the
internal diameter D.sub.i,DS of the top disc 1, is at least 20%,
preferably at least 50%, greater than the internal diameter
D.sub.i,DS of the top disc 1. The top disc 1 forms a top guiding
surface 8 for the flow channel 5, an angle .alpha..sub.DS which
opens out towards the inlet opening 4 and is formed between a
tangent T.sub.1 on the top guiding surface 8 at the inlet to the
suction opening 4 of the top disc 1 and a tangent T.sub.2 on the
top guiding surface 8 at the outlet from the flow channel 5 on its
radially outer air outlet side 5b, being at least 30.degree.. The
maximum value of this angle can be 90.degree., preferably
75.degree.. In the first configuration, the tangent T.sub.1 runs
parallel to the longitudinal axis X-X of the radial impeller 1. In
this way, according to the disclosure the flow is diverted in such
a favourable aerodynamic manner from the axial direction into a
radial or diagonal direction that the efficiency .eta. increases
while the advantages of conventional cylindrical rotors are
retained.
[0048] This is also the case when the tangent T.sub.1 deviates from
the parallel course to the longitudinal axis X-X of the radial
impeller 1 by an angular value .alpha..sub.DS1 of up to
.+-.30.degree., but preferably by only up to .+-.5.degree., as
shown by the second configuration according to FIG. 6. An angle
which opens out towards the inlet opening 4 and is formed between
the tangent T.sub.2 on the top guiding surface 8 at the outlet from
the flow channel 5 on its radially outer air outlet side 5b and the
longitudinal axis X-X of the radial impeller 10 is denoted by
reference sign .alpha..sub.DS2. Thus, the following equation
applies to the angle .alpha..sub.DS claimed according to the
disclosure:
.alpha..sub.DS=.alpha..sub.DS2-.alpha..sub.DS1.
[0049] Analogously to the guiding surface 8 on the top disc 1, the
bottom disc 3 can also form a bottom guiding surface 9 in the flow
channel 5.
[0050] The top guiding surface 8 and/or the bottom guiding surface
9 of the flow channel 5 can particularly be constant in curvature,
as shown in the drawing, except in the case of the bottom disc 3 of
the configuration in FIG. 4, which advantageously counteracts the
formation of flow turbulence.
[0051] Instead of the above-mentioned distance, measured axially in
the direction of the longitudinal axis X-X, between bottom disc 3
and top disc 1, FIGS. 1, 2 and 5 show in the flow channel 5, a
shortest distance in each case, respectively designated by
reference sign A, which preferably varies between air inlet side 5a
and air outlet side 5b of the flow channel 5, between bottom disc 3
and top disc 1. It can advantageously be provided that this
distance A decreases in direction S from the radially inner air
inlet side 5a to the radially outer air outlet side 5b,
particularly while considering the blade spacing determined by the
number of blades 2 such that the cross section of the respective
flow channel 5 also tapers. This is shown in particular in FIG. 5
in which this preferred configuration is compared with a
hypothetical channel configuration which is indicated by a dash-dot
line and for which this distance A is constant. As indicated in the
drawing by the word "constant", in the hypothetical configuration,
which, although possible in the context of the disclosure, is not
preferred, the top guiding surface 8 and the bottom guiding surface
9 run at an equal distance from one another.
[0052] As far as the installation is concerned in a fan unit 20
according to the disclosure, of a radial impeller 10 according to
the disclosure, shown by way of example in FIGS. 3 to 5, various
technical measures relating to the nature of this installation can
optionally further advantageously contribute to the achievement of
an increase in the efficiency .eta. while retaining a high power
density L and a low total sound power level L.sub.W.
[0053] Thus, it can be provided in particular that an inlet 21 of
the housing 7 for the radial impeller 10 is nozzle-shaped, the
inlet 21 of the housing 7 dipping in particular into the suction
opening 4 in the top disc 1, as shown most clearly in FIG. 3, but
also in FIGS. 4 and 5.
[0054] This configuration contradicts the expert view that an
improvement in the efficiency .eta. cannot be expected of a
nozzle-shaped top disc, as is usual in radial fans having
backward-curved blades.
[0055] In the case of known radial fans having forward-curved
blades, the nozzles do not dip into the top disc. In known radial
rotors having forward-curved blades, the static pressure difference
at a gap between the nozzle-shaped inlet and the top disc is too
small in order for said difference to apply the main flow, moving
axially along the longitudinal axis X-X through the inlet, to the
top disc by an impulse supply from the split flow also passing
laterally through the gap into the suction opening in the top disc.
Furthermore, as a result, the blades are subjected to an axial
onflow near the top disc, as a result of which the flow is
separated at the blade inlet edges.
[0056] However, instead, these disadvantages can be avoided in the
disclosure by the gap 22 formed by dipping the nozzle-shaped inlet
21 into the suction opening 4 in the top disc 1 over the dipping
length L.sub.E. In this respect, the dipping length L.sub.E of the
gap 22 can be within a range of 0.5% to 5.0%, preferably within a
range of 1.0% to 3.0% of the external diameter D.sub.a,DS of the
top disc 1 and a gap width S.sub.W of the gap 22 can be within a
range of 0.5% to 5.0%, preferably 1.0% to 3.0% of the external
diameter D.sub.a,DS of the top disc 1.
[0057] It has proved to be extremely favourable for the formation
of the flow downstream of the inlet 21 if an inner radius R.sub.i,S
on the leading edge 2a of the blades 2 (see FIG. 2) in the vicinity
of the top disc 1 is greater than or equal to the inner radius
R.sub.i,DS of the suction opening 4 of the top disc 1 (see FIG.
3).
[0058] Furthermore, as shown in FIG. 3, it can preferably be
provided that a ratio V.sub.B of a width B of the housing 7 at the
air inlet opening 7b thereof into the air guidance channel 7a to an
impeller outlet width b.sub.2 of the radial impeller 10 at the
radially outer air outlet side 5b of the flow channel 5 has a value
within the region of 1.0.ltoreq.V.sub.B.ltoreq.1.4. As a result,
while avoiding losses of the total pressure .DELTA.p.sub.t, the
conversion of dynamic pressure into static pressure is promoted.
The secondary flow in the housing 7 is positively influenced due to
a configuration of this type of the housing 7 with a small increase
in width according to the stated ratio V.sub.B, which, contrary to
expert opinion, leads to a significant increase in the efficiency
.eta.. In this respect, it is particularly advantageous if the
impeller outlet width b.sub.2 at the radially outer air outlet side
5b of the flow channel 5 assumes a value which is at most 70% of
the overall width b.sub.ges of the radial impeller 10.
[0059] Finally, from the point of view of a high efficiency .eta.,
it is also advantageous if the housing 7 has an air guidance
channel 7a, wound spirally around the radial impeller 10, not with
a rectangular, but with an oval, preferably elliptic cross section
which increases constantly from the side of the radial impeller 10.
In an elliptic cross section of this type, the ratio of the large
to small semi-axis of the ellipse can preferably be within a range
of 1.2 to 3.0, it being possible for the large semi-axis to be
oriented in a different manner, for example preferably vertically
or horizontally.
[0060] The disclosure is not restricted to the illustrated and
described embodiments, but also includes all configurations which
have the same effect within the meaning of the disclosure. Thus, a
person skilled in the art can also provide expedient additional
technical measures without thereby departing from the scope of the
disclosure. For example, it can advantageously be provided that an
outlet diameter D.sub.a,S of the blades 2 on the top disc 1 is less
than or equal to the external diameter D.sub.a,DS of the top disc
1. It can also be provided that this outlet diameter D.sub.a,S is
less than or equal to the external diameter D.sub.a,BS of the
bottom disc 3.
[0061] It has already been stated that the top guiding surface 8
and/or the bottom guiding surface 9 of the flow channel 5 can be
curved in a constant manner. The same preferably also applies to
the respective pressure sides 2c and suction sides 2d of the blades
2, the above wordings " . . . at least in part" and "curved in a
concave manner at least in regions" (or "curved in a convex manner
. . . ") meaning that the respective curvatures can also comprise
straight portions, particularly at the ends thereof.
[0062] If the radial impeller 10 is arranged in the housing 7
coaxially with an electric drive motor 6, as shown in FIGS. 3 and
5, an outer contour 6a of the drive motor 6 can engage positively
in a motor receiving opening 3a (most clearly visible in FIG. 2) of
the bottom disc 3 or alternatively it can also be covered by a
full-surface bottom disc 3, the bottom disc 3, preferably together
with the contour 6a of the motor 6 received in its motor receiving
opening 3a, having a dome-shaped form. When a motor 6 is used in
the impeller region, burbling from the motor contour and backflow
in the downstream region can be prevented by a dome shape of this
type of the bottom disc 3. This is evident, for example, by
comparing FIGS. 3 and 5 with FIG. 4, FIG. 4 showing the undesirable
formation of vortices W in a wake space between motor 6 and bottom
disc 3.
[0063] A twin-flow configuration of the radial impeller 10
according to the disclosure is also possible, without departing
from the scope of the disclosure.
[0064] Furthermore, the disclosure can also be defined by any other
combination of particular features of all individual features
disclosed overall. This means that in principle, practically every
individual feature can be omitted or replaced by at least one
individual feature disclosed elsewhere in the application.
[0065] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the disclosure. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the disclosure, and all such modifications are intended to be
included within the scope of the disclosure.
LIST OF REFERENCE SIGNS
[0066] 1 top disc of 10 [0067] 2 blades of 10 between 1 and 3
[0068] 2a leading edge of 2 [0069] 2b trailing edge of 2 [0070] 2c
pressure side of 2 [0071] 2d suction side of 2 [0072] 3 bottom disc
of 10 [0073] 3a motor receiving opening for 6 in 3 [0074] 4 suction
opening of 1 [0075] 5 flow channel in 10 between 2/2 and between
8/9 [0076] 5a air inlet side of 5 [0077] 5b air outlet side of 5
[0078] 6 drive motor for 10 [0079] 6a outer contour of 6 [0080] 7
housing of 20 [0081] 7a air guidance channel of 7 [0082] 7b air
inlet opening of 7 into 7a [0083] 8 top guiding surface of 5 [0084]
9 bottom guiding surface of 5 [0085] 10 radial impeller [0086] 20
fan unit with 10 [0087] 21 inlet of 7 [0088] 22 gap between 21 and
1 [0089] A shortest distance between 1 and 3 [0090] B width of 7 at
7b [0091] b.sub.2 impeller outlet width of 1 [0092] b.sub.DS width
of 1 [0093] b.sub.ges overall width of 10 [0094] D.sub.a,BS
external diameter of 3 [0095] D.sub.a,DS external diameter of 1
[0096] D.sub.a,S outlet diameter of 2 at 1 [0097] D.sub.i,DS
internal diameter of 4 in 1 [0098] d.sub.S profile thickness of 2
[0099] LR running direction of 10 [0100] L.sub.E dipping length of
21 into 1, length of 22 [0101] L.sub.S profile overall length of 2
[0102] R.sub.i,S inner radius of 2 at 2a [0103] R.sub.i,DS inner
radius of 4 in 1 [0104] S flow direction in 5 from 5a to 5b [0105]
T.sub.1 tangent on 8 at 4 [0106] T.sub.2 tangent on 8 at 5a [0107]
W vortex between 3 and 6 (FIG. 4) [0108] X-X longitudinal axis of
10, 20 [0109] .alpha..sub.DS angle between T.sub.1 and T.sub.2
[0110] .alpha..sub.DS1 angle between T.sub.1 and X-X [0111]
.alpha..sub.DS2 angle between T.sub.2 and X-X
* * * * *